Is Icloud storage credit card security code request legit?

After a few years of acceptable credit card payment for Icloud storage I recived an email from "iTunes Store" <do_not_reply@itunes.com>", asking me to update my credit card info. Looking further via my Iphone, it seems they want my credit card (AMEX) security code. After so many monthly renewals, does that sound legit? If I ebnter the security code via my IPhone, isn't that OK?

Thanks